If your doctor is clueless, that doesn't bode well. hmmm... a 20 pound gain in 3 months is really unusual if you haven't been eating that much. To really gain 20 pounds of fat, you'd have to have been eating an enormous amount of food in those three months. So, something else must be going on.
Are you on any birth control pills ? I have friends who changed their BC and as a result, gained weight. Not fat. they packed on water. if you're on any medications, meds can cause unexplained weight gain.
Can a woman gain 5 pounds of muscle in three months ? Not out of the realm of possibility, but it means you have to have been extra calories plus engaging in a strenuous strength training workout.
I guess you're going to have to watch for any symptoms of any kind, just in case. Of course, if your doctor says you're in good health, then maybe everything is okay and your weight will stabilize.
PS - Yes, water can accumulate over a few weeks too. it varies. 2018 days ago